Energy efficient coal power station
How can a coal power station be more energy efficient? Can a turbine be made to produce more electricity from the heat, or can the heat be reused somehow?
Answer from Green Energy Efficient Homes
Most coal power stations are quite inefficient, converting only about around 30% of the heat energy in coal into electricity. There are a number of reasons for this. First off, the theoretical efficiency of a Rankine cycle engine - the type of engine used in power plants where water converted to steam is used to drive a turbine - is limited to about 63% under ideal conditions. Typical peak efficiency of a well built coal-fired power station is closer to 40% with many actual plants operating far below that.
There are a number of ways in which a coal power station could be made more efficient. For example, the waste heat in the form of steam could be captured and used to heat adjacent buildings. This is called regenerative heating (because the waste heat is being 'regenerated' into something useful elsewhere). Better engines that come closer to the theoretical peak efficiency can be installed to replace older inefficient engines.
Another big source of waste in coal power stations is the fact that they cannot respond rapidly to changes in demand. If 500,000 homes decide to turn on their oven or dryer all at the same time, a coal power station can't instantly start generating 500 more megawatts of electricity as it can take as much as several hours to get the extra capacity. As a result, coal power stations are frequently ramped up to what is predicted to be the peak load, based on historical usage, weather forecasts, and other factors. Electricity that isn't needed isn't generated, but the heat is still produced, and as a result there can be considerable wasted energy in a coal power station that is producing more heat than is needed to supply peak demand.
The peak power issue applies to many renewable sources of power as well. You can't ramp up wind power or solar electric power to meet a peak in demand if the wind isn't blowing or the sun isn't shining. Hydro electric power is more responsive to demand changes as you can just increase or decrease the water flow through turbines based on minute-by-minute demand.
Of course if we make coal power stations more efficient, we'd reduce greenhouse gas emissions for each kilowatt of energy produced. But ideally we should be eliminating coal (and all fossil fuels) from our energy mix because of the catastrophic effects of climate change, so while making coal power stations more energy efficient in the short term is probably a good thing, it should definitely not be our primary focus. It would be much better to reduce our energy needs, through conservation (turning off the air conditioner), increased efficiency of energy-using devices (upgrading to an ENERGY STAR air conditioner, buying fluorescent lights rather than incandescent, etc.), and increased efficiency of buildings (better insulation, thermal window coverings and such).
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